When energy is stored for delivery in the form of electrical power, it is typically accumulated in one location as potential energy (chemical, electrostatic, nuclear, etc.) or kinetic energy (flywheel, etc.), and then delivered to a load, as needed. Some applications suggest the use of multiple reservoirs of energy, each of which might be referred to as a “cell,” to be used cooperatively in the manner of a “battery.” Prior art configurations of multiple energy reservoirs include one sort, or another, of electrical coupling among the cells, or mechanical coupling among sources of mechanical energy, whether connected in series or parallel, either permanently or by temporary switching. Electrical coupling among cells presents a number of known drawbacks such as an imbalance for charging purposes if internal cell impedances are mismatched, and system failures in case individual cells become open or shorted. Moreover, electrical coupling of multiple cells may not lend itself to readily swapping out failed cells, or accommodating the overall system to changes in the capacity, or other operating characteristics, of individual cells.